[Effects of Enzyme Activities and Metabolomics of Wheat Rhizosphere Soil Under Biodegradable Microplastics]

To investigate the effects of biodegradable polylactic acid microplastics （PLA-MPs） on soil enzyme activities and metabolomics in wheat rhizosphere， a pot experiment was conducted with a control group （CK）， three abundance levels （0.1， 0.5， and 1 g·kg^-1）， and two particle sizes （150 μm and 1 000 μm） of PLA-MPs. The metabolomic analysis of wheat rhizosphere soil was employed by the thermo fisher scientific UHPLC-Q exactive， and the differential metabolites were integrated to screen by the principal component analysis （PCA） and orthogonal partial least squares-discriminant analysis （OPLS-DA）. The results showed that compared to those under CK， soil urease （S-UE）， acid phosphatase （S-ACP）， and sucrase （S-SC） activities exhibited significant increasing trends （P<0.05） under different PLA-MPs abundances and particle sizes， with particle size demonstrating a more pronounced effect than that of abundance. In contrast， no significant differences were observed in soil dehydrogenase （S-DHA） and catalase （S-CAT） activities. PCA and OPLS-DA of rhizosphere soil metabolites revealed clear distinctions among treatments. Differential metabolites under varying PLA-MPs sizes and abundances predominantly belonged to carboxylic acids and derivatives， prenol lipids， fatty acyls， organooxygen compounds， sterols and derivatives， and glycerophospholipids. Compared to that in CK， the expression levels of differential metabolites varied across treatments. For instance， under the 0.1 g·kg^-1 abundance treatment， metabolites such as citral propylene glycol acetal and surfactant maintained relatively high expression levels （0.410 3 and 0.415 3， respectively）， while the top 20 abundance-ranked differential metabolites under the 1 000 μm particle size treatment showed lower relative expression. KEGG pathway analysis of soil differential metabolites indicated both differences and similarities across PLA-MPs sizes and abundances. The CK vs. 150 μm treatment exhibited the highest number of significantly altered metabolic pathways （165）， whereas other treatments showed fewer. Major significantly altered pathways included porphyrin and chlorophyll metabolism， caffeine metabolism， and butanoate metabolism. Interactive effects were observed between differential metabolites and enzyme activities； for example， L-arabitol showed significant correlations with S-UE （r = 0.526， correlation coefficient， id.）， S-ACP （r = -0.699）， and S-SC （r = -0.784）， while linoleamide and oleamide exhibited a significant positive correlation （r = 0.777）. This study provides foundational data and theoretical insights for assessing the potential ecological risks of PLA-MPs in soil ecosystems.